JPH02128813A - Method of molding polytetrafluoroethylene polymer stretched molded product - Google Patents

Abstract

PURPOSE:To contrive an improvement in yield of the final molded product to a PTFE foundation by a method wherein a ratio between an area of a hollowed part and that of a PTFE foundation part is specified, the hollowed part of the PTFE foundation part is filled with a thermoplastic polymer whose viscosity is lower than that of the PTFE foundation and stretching molding of the same is performed. CONSTITUTION:The interior 12 of a compression die 11 is heated at a fixed temperature beforehand and a PTFE foundation controlled at the fixed temperature is put between compression dies 11 together with a thermoplastic polymer 5. A lubricant is caused to exist on the interior 12 of the compression die, the PTFE foundation 1 is compressed, which is caused to plug-flow along with the thermoplastic polymer 5 for stretching. After the same is cooled down to the fixed temperature or lower by applying compression force to the same as it is, the die 11 is broken and the stretched PTFE 13 is taken out together with a stretched thermoplastic polymer 14. When the cylindrical PTFE foundation whose central part is hollowed out is filled with the thermoplastic polymer 5 and stretched under pressurization, the same becomes the PTFE sheet 13 which is stretched biaxially in an almost concentric state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] Due to its outstanding properties, polytetrafluoroethylene is currently one of the important industrial materials. In particular, PTFE is used in the fields of sealing materials and lining materials for gaskets, packings, etc. due to its chemical resistance, heat resistance, cold resistance,
It is widely used as molded products in various shapes due to its excellent properties such as low friction, non-staining, non-adhesive, and electrical insulation properties.

The present invention uses polytetrafluoroethylene polymer (PT
(abbreviated as FE).

In particular, molded products manufactured by the molding method of the present invention have excellent creep resistance and gas barrier properties, and can be suitably used as sealing materials such as gaskets and packings, sliding members such as piston ring bearings, and the like.

[Conventional technology]

The melt viscosity of normal thermoplastic resin at the molding temperature is 1
However, polytetrafluoroethylene has a high viscosity of IQI 1 poise even at 380° C., which is higher than its melting point (327° C.), and is difficult to mold using molding methods such as melt extrusion and injection molding.

For this purpose, the molded product is produced by - A method in which the powder is preformed in the membrane by compression etc. and then heated and sintered to a temperature above the melting point (compression molding method, ram extrusion method, paste extrusion method, etc.)
Alternatively, the base material formed in this process is further manufactured by cutting, cutting out the cut product, punching, stretching (roll rolling method, tension stretching method), etc.

Furthermore, in the field of gasket materials, gaskets containing fillers such as glass fiber, graphite, carbon fiber, and zirconium oxide are also manufactured.

The heat resistance temperature of polytetrafluoroethylene is generally 260
'C, but when used as a sealing material for gaskets, etc., compression resistance and mechanical strength to withstand external forces are required, and depending on the structure, shape, and purpose, the maximum usable temperature is 260℃ or higher. The temperature is quite low. This is due to the inherent property of polytetrafluoroethylene that it tends to creep under load, and of course, the higher the temperature, the more likely it is to creep.

In the field of corrosion-resistant gasket materials, improvements have been made to improve compression creep resistance, such as adding fillers or structurally combining low-creep materials with polytetrafluoroethylene or filled polytetrafluoroethylene. However, all of them have problems such as insufficient compression creep resistance at high temperatures and low chemical resistance.

In addition, sealing materials other than gaskets, such as valve seals (ball valve seats, Kate valve seats, etc.)
Polytetrafluoroethylene is also used when corrosion resistance is required for other dynamic sealing materials (gland packing, U packing, V packing, etc.), but it is also desired to improve compression creep resistance. .

On the other hand, polytetrafluoroethylene is also important as a corrosion-resistant lining material, but it tends to cause blistering, which may cause problems in reliability as a corrosion-resistant lining. Blistering is a phenomenon observed in gas-phase fluid piping, and there is a desire to improve the blister resistance.

The present inventors have already reported the superiority of biaxially oriented polytetrafluoroethylene sheets as an improvement over these problems in Japanese Patent Laid-Open No. 63-239019 (Japanese Patent Application No. 62-61302), It was proposed in Application No. 62-71370.

As a result, the present invention provides a molding method that can efficiently mold sealing materials, sliding members, etc. made of these biaxially oriented sheets.

[Problem to be solved by the invention]

The problem to be solved by the present invention is the punching that occurs during processing such as punching and cutting when manufacturing a molded product having a hollowed-out center portion such as a gasket, piston ring, or bearing from the biaxially oriented sheet. The objective is to reduce loss, cutting debris, etc. and improve the yield of the final molded product relative to the original PTFE base material.

Generally, sealing materials such as gaskets and packings, and sliding members such as bearings have a ring shape or a disk shape with a circular center portion. Therefore, from the biaxially oriented sheet,
When obtaining a final molded product with a hollowed-out center portion, the hollowed out portion becomes a loss, and the yield of the final molded product relative to the PTFE base material becomes low. PTFE is an expensive resin, and the lower the yield, the lower the economic efficiency.

As a method for solving this problem, it is conceivable to use a hollowed-out PTFE base for obtaining the biaxially oriented sheet. However, even if an attempt is made to stretch the hollowed-out PTFE base material under pressure into at least two wheels as it is, it will not undergo similar deformation due to the hollowed out portions, making it impossible to obtain a biaxially oriented sheet in the desired shape.

Therefore, currently, final molded products such as gaskets are obtained from the biaxially oriented sheet through processing such as punching and cutting.
The yield of the final molded product based on the original plate is low, and the economical efficiency is also low.

Furthermore, when the biaxially oriented sheet is molded by compression molding using a press molding machine, the maximum dimension of the sheet obtained is determined by the total compression force of the press, and therefore the final molded product such as a gasket obtained from the sheet is The outer diameter of the metal is also limited.

Therefore, it is an object of the present invention to make it possible to obtain a final molded product having a larger outer diameter with the same compression force.

[Means for Solving the Problems] The present inventors have completed the present invention as a result of intensive studies to develop a molding method that solves the above problems.

That is, the present invention provides: A polytetrafluoroethylene polymer base is prepared in a die by lubricating the interface between the inner surface of the die and the base, and the base is rotated at least biaxially under pressure at a temperature equal to or higher than the glass transition temperature of the base. (1) The substrate is a sheet of PT with its center hollowed out before stretching.
(2) the ratio of the area of the hollowed out portion to the area of the PTFE substrate is 1:19 to 9:1, and (3) the PTFE substrate is applied to the hollowed out portion during molding. A method for forming an oriented PTFE article, which comprises placing the PTFE substrate in a die filled with a thermoplastic polymer having a viscosity lower than the viscosity of provide.

The molded product described in the present invention is a molded product having a relatively simple shape such as a film, sheet, or disk shape, with the center portion of the molded product being hollowed out.

The wall thickness of these molded products is arbitrarily determined depending on the purpose, but is preferably 301 mm or less, more preferably 0.05 mm or more and 10 mm or less.

PTFE referred to in the present invention refers to tetrafluoroethylene (
A homopolymer of TFE (hereinafter abbreviated as TFE) or a copolymer containing TFE as a main component, that is, TFE
A copolymer containing 0 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more, or a blend polymer consisting of them, preferably an ultra-high molecular weight polymer having a number average molecular weight of 106 to 10@ It is. Especially T
An ultra-high molecular weight homopolymer of FH is preferred.

Monomer components to be copolymerized with TFE include perfluoroalkyl vinyl ether, hexafluoropropylene, ethylene, chlorotrifluoroethylene, vinyl fluoride, vinylidene fluoride, trifluoroethylene, perfluorobutadiene, perfluoroolefin, perfluoroalkyl. Acrylic acid esters, propylene, etc. are preferred.

In addition, the above PTFE is used as the main matrix resin component, and as reinforcing materials, inorganic fillers such as carbon fiber, graphite, carbon, molybdenum disulfide, bronze, zirconium oxide, and zirconium silicate, and aromatic polyamide fibers and aromatic polyester fibers are used. A filler-containing PTFE composition containing at least 60% by weight of at least one organic filler such as PTFE (
The scope of the present invention also includes compositions in which other thermoplastic resins and various compounding agents are added in an amount of 10 parts by weight or less per 100 parts by weight of TFE homopolymer or copolymer.

PTFE ultra-high molecular weight material can be used particularly well in the molding method of the present invention. This material is generally a powder, which is compacted under high pressure by compression molding at room temperature, then at a high temperature (-
above the melting point temperature of PTFE, preferably in the range of 340 to 400°C in the case of polytetrafluoroethylene)
A molded product having a specific gravity of preferably 1.8 or more, more preferably 2 or more is obtained by sintering the product, and this is used as a PTFE base and oriented in at least two rings.

The oriented PTFE molded article of the present invention is oriented at least biaxially. The present invention will be explained below using a sheet-like molded product as an example.

There are three types of sheet stretching: uniaxial stretching, biaxial stretching, and multiaxial stretching.
Although there are various embodiments, the oriented PTFE sheet of the present invention is biaxially stretched or multiaxially stretched.

The molding method of the present invention is suitable for molding sheets having an area ratio and a stretching ratio of twice or more of the oriented PTFE molded product.

Biaxial stretching or multiaxial stretching of super high polymer IJPTFE improves compression creep resistance. As a result of a detailed study on the relationship between stretching ratio and compression creep resistance, molded products with a stretching ratio of 2 times or more have significantly superior compression creep resistance.

Stretching under pressure in a die means stretching the PTFE base material in a compression die or an extrusion die in compression molding or extrusion molding by causing a plug flow due to compression force or extrusion force. The term "plug flow" here includes states similar to that. Also, in order to cause plug flow, at least the inner surface of the die or PTFE
It is necessary to have a lubricant present on the substrate surface.

In the case of ultra-high molecular weight PTFH, the PTFE base refers to a molded product made through the general process of pre-compression molding → firing → cooling of molding powder.

The shape of the PTFE base material used in the present invention is a sheet shape, and the center portion thereof is hollowed out. Specific examples include, but are not limited to, preferred PT shapes as shown in FIG.
The shape of the FE base material, when viewed from above in FIG. 1, is similar to the shape of the final molded product. Particularly preferred is a shape like (1-3).

In FIG. 1, 1 indicates the PTFE base material, and 2 indicates the hollowed out portion.

Effects (effects) of using a hollowed-out PTFE base
is particularly noticeable when a compression press molding machine is used. That is, when the biaxially oriented sheet is molded using a compression press molding machine, the maximum dimension of the sheet obtained is determined by the total compression force of the press, and therefore The outer diameter of the final molded product such as a gasket obtained from the sheet is also limited.

Therefore, one of the effects of the present invention is that a final molded product with a larger outer diameter can be obtained using a press molding machine with the same compression force.

In the PTFE base material, the area of the hollowed out part and P
It is necessary that the area ratio of the TFE base portion is 1:19 to 9:1. If the area of the hollowed out portion is smaller than 1/19 of the area of the PTFE base portion, the yield improvement effect will be reduced, which is not preferable.

Furthermore, if the area of the hollowed out portion exceeds 9 times the area of the PTFE base portion, problems such as breakage, twisting, and buckling of the PTFE cell portion during stretch molding may occur, which is undesirable. is the hollowed out part and PT
The area ratio of the FE base portion is in the range of l:9 to 8:2, particularly preferably in the range of 2:8 to 7:3.

In the molding method of the present invention, the amount of thermoplastic polymer to be filled into the hollowed out part of the PTFE base material may be an amount that substantially fills the hollowed out part. Thermoplastic polymer in a volume of 80-110% of the volume of the part, particularly preferably 90-105%
Filled with a volume of thermoplastic polymer and stretch-molded.

The shape of the thermoplastic polymer filled in the hollowed out portion may be any shape, such as pellets, powder, or preformed sheet.

In the molding method of the present invention, the viscosity of the thermoplastic polymer filled in the hollowed out portion of the PTFE base must be lower than the viscosity of the PTFE base during stretch molding. When trying to fill the hollowed out part with a thermoplastic polymer having a viscosity equal to or higher than that of the PTFE base and stretching it under pressure, or when stretching the PTFE base without the hollowed out part as it is. The deformation resistance is equal to or higher than that of the PTFE substrate, the stretching ratio becomes low, and the effect of using the hollowed out PTFE substrate is lost, which is not desirable.Preferably, the viscosity is lower than the viscosity of the PTFE substrate during stretch forming. A thermoplastic polymer having a melt index under a C12,16 kg/Ca load of 10 g/10 minutes or less, particularly preferably a viscosity of 1/2 or less of the viscosity of the PTFE base during stretch molding,
In addition, the thermoplastic polymer has a melt index of Ig/10 minutes or less at 190°C and a load of 2.16 kg/cd. Melt index is measured according to ASTM D-1238. In addition, the viscosity of the thermoplastic polymer used for the PTFE base material and filling is RHEOMETRIC 3, DYNAl'llCSPECTROMETEI?
Measured using DS-7700 or the like.

In the molding method of the present invention, there is no particular limitation on the type of thermoplastic polymer to be filled into the hollowed out portion of the PTFE base. Specifically, polyethylene, polypropylene, poly-4-methylpentene-1, polybutene-1, vinyl chloride resin, vinylidene chloride resin, polystyrene, ABS resin, AS resin, AAS resin, ABS resin, polyvinyl alcohol, polyvinyl butyral, Acrylic resin, thermoplastic polyurethane, fluororesin (low molecular weight PTFE, P
FA, FEP, PVdF, ETFB, PCTFE, etc.)
, polycarbonate, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate,
Polyethylene terephthalate, polyphenylene sulfide, polysulfone, polyether sulfone, polyetherimide, polyarylate, polybutadiene, styrene-butadiene random copolymer, styrene-butadiene block copolymer, styrene-ethylene-butylene blank copolymer , olefinic thermoplastic elastomer,
Examples include ester thermoplastic elastomers, urethane thermoplastic elastomers, amide thermoplastic elastomers, and the like. Preferably polyethylene, polypropylene,
Examples include polybutene-1, poly-4-methylpentene-1, and fluororesin. From an economic point of view, thermoplastic polymers, which are cheaper than PTFE, are preferred.

The PTFE base material and the thermoplastic resin to be filled are preheated to 150° C. or higher prior to stretching. The preferable preheating temperature is 170 to 340°C, more preferably 200°C.
~327°C.

The temperature may be uniform throughout, but it can also be distributed such that the temperature is higher on the surface layer side and lower on the center side.

The temperature of the die is such that the temperature of the inner surface of the die is 400°C above room temperature.
It can be arbitrarily selected in consideration of moldability and productivity within the following ranges. In particular, if the temperature of the inner surface of the die is less than (temperature of the surface layer of the PTFE substrate - 50) 'C, especially less than (temperature of the surface layer of the PTFE substrate - 100) 'C, the PTFE substrate should be placed on the die prior to molding. If the inner surface of the die and the entire lower surface of the substrate come into direct contact between the time it is placed and the time when it is oriented under pressure, only the lower surface will be exposed to 2. The temperature difference between the top and bottom surfaces of the PTFE substrate becomes large due to rapid cooling, and the top and bottom surfaces are no longer evenly oriented, so a method for reducing the temperature difference is required.

As a method, for example, as shown in Fig. 2 (2-1), the PTFE base steel is curved during heating, or as shown in Fig. 2 (2-2), protrusions 6 are formed on the die surface 3. The PTFE base 1 is placed on the PTFE base 1 by a method using a jig, for example, a metal thread 7, to hold the PTFE base 1 floating on the base steel as shown in Fig. 2 (2-3). There is a method in which the entire lower surface of the die is in direct contact with the inner surface of the die to prevent only the lower surface from being rapidly cooled.

(PTFE filled with thermoplastic polymer in the hollowed out part)
When stretching the base material, use PT as shown in (3-1) in Figure 3.
The FE substrate and the steel plastic polymer 5 can be placed in a die as they are and stretched under pressure.

Furthermore, if the surfaces of the PTFE base 1 and thermoplastic polymer 5 are coated with a thin sheet or film 4 of thermoplastic resin or PTFE as in (3-2), the lubricant adhering to the surface will be removed. This is preferred because it can be easily removed.

Alternatively, as in (3-3), the upper and lower sides are laminated with PTFE sheets 8, and then a thin sheet or film 4 of thermoplastic resin or PTFE is laminated and covered, as in (3-4), in place of the PTFE sheet 8. It is preferable that the PTFE substrate 1 is laminated with a thermoplastic resin sheet 9 and then stretched using the method of laminating and covering with the sheet or film 4, since the sheets 8 and 9 act as a heat insulating layer, so that the PTFE base 1 can be stretched more uniformly.

In addition, as shown in (3-5) and (3-6), a resin sheet 10 is placed between the PTFE bases 1 to provide a friction force greater than that between the PTFE bases, and a thermoplastic polymer 5 is used inside. Stretching is preferable because a plurality of stretched sheets can be obtained at one time, which improves productivity.

When orienting under pressure, 50%
kg/ct or more pressure, preferably 500 kg/ct
cd or more, more preferably 1.000 kg/cr
A high pressure of i or more and 4,000 kg/ci or less is applied to orient.

In order to have a lubricant on the inner surface of the die, in the case of compression molding, it is generally applied before molding, and in the case of extrusion molding, it is either press-fitted into the extrusion die from the outside or applied before molding. is common.

As the lubricant, silicone oil with excellent heat resistance is suitable.

Stretching under pressure in a die described in the present invention refers to compression/pressure drawing in a compression die, extrusion/pressure drawing in an extrusion die, etc., which will be explained below using the figures. do.

In FIG. 4, at least the inner surface 12 of the compression die 11
is preheated to a certain temperature. The PTFE base material, which has been adjusted to a constant temperature, is placed between the heated compression die 11 together with the thermoplastic polymer 5 (4-1). At this time, a lubricant is present on the inner surface 12 of the compression die, and the PTFE substrate 1 is compressed and stretched by plug-flowing together with the thermoplastic polymer 5 (4-2), and the compression force is applied as it is to keep the temperature below a certain level. After cooling, the die 11 is opened and the drawn PT
The FE 13 is taken out together with the stretched thermoplastic polymer 14.

When a cylindrical PTFE base with a hollow center as shown in (4-3) is filled with thermoplastic polymer 5 and stretched under pressure according to the molding method of the present invention, (4-4) The PTFE sheet 13 is stretched into two substantially concentric circles as shown in FIG. When a laminated PTFE base is used as the PTFE base, a molded article can be obtained by peeling off the stretched laminated PTFE sheet.

On the other hand, FIG. 5 shows the shape of a molded sheet when stretch molding is performed without filling the hollowed out portion 2 of the PTFE base 1 with the thermoplastic polymer 5.

Using the same PTFE substrate 1 as in Figure 4 (4-3),
When stretched under pressure under the same conditions as shown in the figure without using the thermoplastic polymer 5, the inner and outer peripheries do not have a circular shape as shown in (5-4), and the sheet 15 has a distorted shape and is uniform. The shape 16 of the hollowed out portion 2 after stretching is not circular like 14 in FIG. 4 (4-4), and the area of 16 is smaller than 14. Further, the outer diameter of the seam 5 after stretching is smaller than the outer diameter of 13 in (4-4).

Here, 17 is the outer circumference of the stretched sheet 13 in (4-4),
18 indicates the inner circumference. (5-5) is the final molded product obtained from 15, but it can be seen that only the final molded product with smaller external dimensions and area can be obtained than (4-5).

FIG. 6 shows an extrusion apparatus in which the method of the invention can be used.

In FIG. 6, a ram extrusion molding machine 21 consisting of a prismatic heating cylinder 19 with an internal square cross section and a square ram 20 has a hollowed-out center portion shown in the present invention, and a thermoplastic polymer is inserted therein. A PTFE base 1 filled with PTFE 5 is put therein and extruded into a die 22 while being heated by a ram 20. die 2
In the middle of part A of 2, in order to apply lubricant to the interface between the surface of the PTFE substrate 1 and the die surface, there is a series of devices for oozing lubricant.

The high-pressure lubricant is guided from the lubricant introduction path 23 to the plurality of seepage ports 24, seeps out onto the surface of the PTFE base material, and applies the lubricant to the interface between the surface of the molded body and the surface of the die.

The lubricant seepage port 24 is made of a material having a small slit shape or a fine communicating hole such as sintered metal, and the lubricant seeps out from the fine hole. Alternatively, it is also possible to apply a lubricant to the inner surface of the die by spraying or the like before molding.

The PTFE substrate whose surface is uniformly coated with lubricant exhibits a so-called plug flow in which the entire PTFE substrate flows at approximately the same speed within the die 22. Next, in the B part of die 22,
Stretch the plug flow PTFE substrate. B of die 22
The portion has a structure in which the thickness of the PTFE substrate is reduced.

The flow change of PTFE in part B during biaxial stretching is shown in the seventh figure.
Shown in the figure. The PTFE base material is simultaneously pushed out in the flow direction and in the direction perpendicular to the flow direction in the direction of the two wheels while maintaining the plug flow.
Multiaxially stretched. The force for stretching the PTFE substrate is exerted by the force extruded from a ram extruder 1 m21. The biaxially stretched PTFE green body is cooled in section C of the die and exits the die 22.

The biaxially stretched PTFE is taken off by a roll 25. When a laminated PTFE base is used as the PTFE base, a molded article is obtained by peeling off the laminated NPTFE stretched sheet extruded from the die 22.

[Effects of the Invention] The present invention provides a method for converting biaxially oriented PTFE sheets into gas cartridges,
Reduces the loss that occurs during processing such as punching and cutting when obtaining a final molded product with a hollowed-out center part such as a piston ring, bearing, etc., and improves the yield of the final molded product based on the PTFE base plate. , is an economical molding method.

In particular, it is an economically very useful method for forming gaskets made of biaxially stretched PTFE sheets.

PTFE two-wheel stretched sheets are required to have the original properties of PTFE, that is, chemical resistance, corrosion resistance, low friction, non-adhesiveness, and heat resistance, as well as compression resistance and resistance to external forces that are applied during use. Particularly suitable for use in situations where mechanical strength and dimensional stability are required, e.g.
It is suitable as a sealing material for gaskets and packings, and for sliding members such as bearings and piston links.

Example 1 Polytetra consisting of a homopolymer of T'FB produced by the free baking method described in "Fluororesin" (Nikkan Kogyo Shimbun, published in April 1976, pp. 58-65). A fluoroethylene sheet (number average molecular weight lXl0') was used as the PTFE substrate.

The shape of the PTFE substrate is as shown in Fig. 4 (4-3), with an outer diameter of 42011Il, an inner diameter of 300+u+, and a thickness of 10m5.
The shape is as shown in . In addition, as thermoplastic polymers, high-density polyethylene manufactured by Asahi Kasei Corporation, Santic R
620 g of OB 870 (190° C., 2.16 kg/c - melt index under load 0.3 g/10 min) pellets were filled into the hollowed out part of the PTFE matrix. Using these materials, a biaxially oriented PTFE sheet having a hollowed-out center portion was obtained by the compression molding method shown in FIG.

Shin-Etsu Silicone (KF) is used as a lubricant during stretch molding.
965.10,0OOcs) was applied to the inner surface 12 of the compression die 11.

The temperature of the compression die was set at 80°C. polyethylene and P
The TFE substrate was preheated to 300°C using a preheating press provided separately. The base material preheated to 300°C was compressed with a compression die at 80'C, stretched by plug flow, and left under pressure for 10 minutes, and then taken out.

The substrate is stretched uniformly on two wheels as shown in Figure 4 (4-4),
The two wheels are stretched to an area ratio of 3.5 times, and by removing the stretched polyethylene, the outer diameter is 760 mm and the inner diameter is 5.
50mm, thickness 2.86+m, 1 in Figure 4 (4-4)
A biaxially stretched PTFE sheet having a shape as shown in No. 3 was obtained.

From the obtained biaxially stretched PTFE sheet, a product with an inner diameter of 560 mPa and an outer diameter of 745 m+s was obtained by punching. The yield of the product based on the original plate was 88χ.

Comparative Example 1 Using the same PTFE sheet as used in Example 1,
A PTFE base material having the same shape and dimensions as shown in FIG. 5, without using a thermoplastic polymer, and in the same manner as in Example 1 except for that, was stretched with the same compressive force as in Example 1.

As a result, the stretched sheet obtained is 1 in Figure 5 (5-4).
As shown in No. 5, the sheet was non-uniformly stretched, with neither the outer periphery nor the inner periphery being circular.

The maximum dimensions at two points on the outer circumference are 600 mm, the maximum dimensions at two points on the inner circumference are 290 mm, and the thickness is 2.
It was stretched to 90 mm and 3.4 times the area ratio.

From the obtained stretched sheet, an inner diameter of 340 m was punched out.
Only a product with an outer diameter of 470 m was obtained.

Further, the yield of the product based on the original plate was as low as 38χ.

Comparative Example 2 The same PTFE sheet used in Example 1 was prepared so that it had the same area as the PTFE substrate used in Example 1.
It was made into a cylindrical shape with a diameter of 294 mm and a height of 10III11 and made of PTFE. The molding conditions were the same as in Example 1, and the film was stretched with the same compressive force as in Example 1.

The only difference is that the PTFE base has a shape that is not hollowed out in the center.

As a result, the obtained biaxially stretched sheet was approximately circular, 2.93+gm thick, and had a diameter of 540mm! I11
It was stretched 3.4 times in area ratio. The stretched sheet had a smaller outer diameter than that of Example 1.

Example 2 Using the same PTFE sheet as used in Example 1,
The outer diameter is 400mm, the inner diameter is 210mm, and the thickness is 10m5.
The shape shown in Figure 4 (4-3) is P.
It was used as a TFE substrate. In addition, as thermoplastic polymers, ultra-high molecular weight polyethylene manufactured by Asahi Kasei Corporation, Sunfine u-OH900 (molecular weight 330 as measured by viscosity method)
A cylindrical sheet with a diameter of 206 as and a height of 10-1 was filled into the hollowed out part of the PTFE base, and stretched in the same manner as in Example 1 with the same compressive force as in Example 1. , biaxially oriented PT with a hollowed-out center part
An FE sheet was obtained.

The dimensions of the obtained sheet are: outer diameter 730+gs, inner diameter 3
It was 1 ml of 90I, 2.94 mm thick, and had a shape as shown by 13 in FIG. 4 (4-4), and was stretched 3.4 times in terms of area ratio.

From the obtained sheet, the inner diameter was 400 m-1 by punching.
A product with an outer diameter of 715 mm was obtained. The yield of the product based on the original plate was 92χ.

Comparative Example 3 The same PTFE sheet used in Example 1 was made into noodles with a diameter of 400 mm and the same size as the outer diameter of the PTFE base of Example 2.
It was made into a columnar shape with a height of 10++ m and made of PTFE. The molding conditions were the same as in Example 1, and the only difference was that the PTFE substrate was stretched with the same compressive force as in Example 1, and the PTFE base was shaped without hollowing out the center.

As a result, the two-wheel stretched sheet obtained was approximately circular and 4.0 mm thick. Its dimensions are 63 mm in diameter
0 m5, and was stretched 2.5 times in terms of area ratio. Compared to Example 2, only a two-wheel stretched sheet with a smaller outer diameter and a lower stretching ratio was obtained.

[Brief explanation of drawings]

The drawings show compression molding and extrusion molding methods in which the method of the present invention can be successfully used. FIG. 1 shows an example of the shape of a PTFE matrix that can be used in the present invention. FIG. 2 shows a method for placing a polytetrafluoroethylene polymer substrate in a die when the temperature of the inner surface of the die is less than (surface layer temperature of polytetrafluoroethylene polymer substrate −50°C). FIG. 3 shows a PTFE matrix filled with a thermoplastic polymer. FIG. 4 shows the method of obtaining a biaxially oriented sheet by compression molding and the shape of the PTFE substrate, the biaxially oriented sheet obtained, and the stamped product according to the method of the invention. FIG. 5 is a comparative example showing the shapes of a sheet and a punched product obtained when a PTFE base having a hollowed-out center portion was stretched without using the method of the present invention. FIG. 6 and FIG. 7 show the orientation state by ram extrusion molding. l...PTFE base 2...(hollowed portion 3...Die 4...Thin sheet 5...Thermoplastic polymer 6...Protrusion 7...Metal thread 8...PTFE Sheet 9...Thermoplastic resin sheet 10...Resin sheet 11...Compression die 12...Die inner surface 13...Stretched PTFE 14...Stretched thermoplastic resin sheet 15...Distorted Sheet 16...Non-circular hollowed out portion 19...Cylinder 20...Ram 21...Ram extrusion molding machine 22...Die 23...Lubricant inlet 24...Bleeding port 25... ...Roll (+-1) (+-4) Fig. 1 (+-2) (hollowed out part) (+-3)

Claims (1)

[Claims] A polytetrafluoroethylene polymer (abbreviated as PTFE) base material is heated in a die under pressure at a temperature equal to or higher than the glass transition temperature of the base material, with the interface between the inner surface of the die and the base material being lubricated. When stretching the substrate in at least two axes; (1) the substrate is a sheet-like PTFE substrate with a hollowed out center portion before stretching; (2) the area of the hollowed out portion and The area ratio of the PTFE base portion is 1:19 to 9:1, and (3) the PTF is applied to the hollowed out portion during molding.
E Molding of an oriented PTFE molded product characterized by placing the PTFE base in a die filled with a thermoplastic polymer having a viscosity lower than the viscosity of the base and orienting the base by compressive force or extrusion force. Law.